The present invention relates to a fire alarm. Fire alarms are used for the early detection of fire in fire-prone areas, to protect individuals and assets. Fire alarms are typically installed on ceilings and have a round, white housing with a diameter of approximately 10 cm and a height of approximately 7 cm to 10 cm. Due to its function, the housing rests against the ceiling. Fire alarms are industrial, series-production products, and fire alarms of the same type and that are made by the same manufacturer typically look the same. In public traffic areas, the fire alarm on the ceiling is typically recognized immediately as a fire alarm due to the size of its housing. The uniformity of series production and the housing shape are therefore always a compromise between the function of the fire alarm and the user's taste, and the aesthetics of the surroundings.
A light-scattering smoke detector is made known in DE 101 18 913 A1, which includes a light transmitter and a light receiver arranged such that a scattering point is located outside of the light-scattering smoke detector, in an open space, the light-scattering smoke detector including a cover for protecting the light transmitter and the light receiver, and means for distinguishing between smoke and other foreign objects located in a region around the scattering point. The means for distinguishing between smoke and other foreign objects includes a processor for analyzing the time profile of reception signals from the light receiver, it being possible to connect the processor to the light receiver. The technique applied by this light-scattering smoke detector for detecting fire makes it possible to install the light-scattering smoke detector essentially flush with the ceiling. As a result, an important step in terms of installing fire alarms of this type in a non-obtrusive manner has been accomplished. A fire alarm which is installed flush with the ceiling in this manner contrasts distinctly with the surroundings in terms of its color design, in particular when installed in colorful rooms, and is therefore still perceived as a conspicuous, distracting object. To feasibly adapt the color of the cover, which closes the fire alarm to the outside, by using a plastic which has been colored accordingly would result in an endless variety of different styles and the associated enormous logistical requirements. Despite a greater variety of color, an exact match with the color scheme at the installation site cannot be achieved with standardized series production methods. It should also be noted that the color scheme in the surroundings could be changed within the framework of renovation work. A fire alarm with a color that matched upon installation would then be perceived again as a distracting foreign object. The fire alarm cannot be subsequently painted to match the new surroundings, since, in the case of a fire alarm mounted flush against the ceiling without an optical labyrinth, there is a risk that painting it in a careless manner could negatively affect the responsiveness of the fire alarm.
Publication DE 101 18 913 A1 also makes known a light-scattering smoke detector which includes two light receivers or focusing optics for a light receiver for adjusting a defined measurement volume.